1. Field of the Invention
The present invention relates generally to beveling spectacle lenses.
2. Description of the Prior Art
Trimming a spectacle lens, which is necessary so that its contour conforms to the required contour, usually by grinding, forms a sharp cutting edge at the periphery of each of its front and rear faces, possibly with burrs associated with surface treatment of those faces. This is known in the art.
The edge is usually beveled in order to deburr and round it, if only for safety reasons, and so make it less sharp.
Initially carried out as a manual reworking operation, such beveling is now carried out automatically, at least on some grinding machines, and in particular on numerically controlled grinding machines.
During beveling, a particular position set point is applied between the beveling tool and the spectacle lens being worked or, to be more precise, between a shaft supporting the beveling tool and a shaft supporting the spectacle lens, which in practice usually takes the form of two half-shafts with the lens gripped between them.
However, because of inevitable random deformations of the more usual spectacle lenses, and equally inevitable software and hardware inaccuracies of the grinding machines available, for example with regard to the relative position of the support shafts and half-shafts in question, it is currently difficult, if not impossible, to carry out the required beveling reliably and with all the necessary accuracy.
On the contrary, it is by no means rare to observe unwanted spreading of the value across the flat of the bevel, i.e. the width of the bevel, all along the worked edge.
A general object of the present invention is to provide a simple and effective way to overcome this problem, and one which yields other advantages.
To be more precise, the present invention consists firstly in a method of improving the accuracy of a beveling operation applied to a spectacle lens; it further consists in a beveling tool for implementing the method.
The invention provides a method of improving the accuracy of a beveling operation applied to a spectacle lens, wherein compensation means having a capacity for elastic deformation are inserted between, on the one hand, the periphery concerned of either the beveling tool used or the worked spectacle lens and, on the other hand, a support shaft for said tool or said lens.
The invention also provides a tool for beveling spectacle lenses, the tool being of the kind including a hub adapted to enable it to be fitted to a support shaft, at least one working rim constrained to rotate with the hub, and compensation means having a capacity for elastic deformation between an active periphery of the working rim and the hub.
In the present context, the expression xe2x80x9ccompensation meansxe2x80x9d refers to means having a capacity for elastic deformation, i.e. means enabling the intervention of such a capacity for deformation.
In one particular embodiment, the compensation means are operative within the beveling tool itself, for example.
Their capacity for elastic deformation then enables the beveling tool to be deformed if the force applied to it is too high, so that the periphery of the tool assumes a position in space enabling it to be applied optimally to the spectacle lens worked, ensuring interengagement of the beveling tool and the spectacle lens and systematically absorbing any spread in terms of the position of those two members relative to each other.
This achieves the required advantageous result of regularizing the value across the flat of the bevel, which is to the benefit of the quality and the reliability of the corresponding beveling operation.
However, other things being equal, it is possible, if required, to make do with a less rigorously calibrated position of the beveling tool relative to the worked spectacle lens, with the benefit of simplifying fabrication of the corresponding grinding machine.
The compensation means used in this way within the beveling tool also advantageously reduce its inertia, which is to the benefit of the overall dynamics.
Finally, a beveling tool including this kind of compensation means can, if required, be mounted on a support shaft at the same time as another rigid beveling tool, so that the resulting grinding machine can, at will, either ensure faithful and rigorous compliance with a particular position set point or accommodate some modulation of that position set point, with the benefit of flexibility of use to suit the application.
The features and advantages of the invention will emerge from the following description, which is given by way of example and with reference to the accompanying diagrammatic drawings.